Michelangelo's portrait of Cleopatra holding an asp to her breast has been celebrated as an ideal Renaissance composition of an idealized woman. With pearls, braided hair and a slender neck, the last pharaoh of ancient Egypt faces her death by snakebite with a detached, elegant gaze.

Courtesy of the Muscarelle Museum of Art

The reverse side of Michelangelo's drawing, revealed in 1988.

Curators had suspected there was another Michelangelo sketch on the black-chalk drawing's reverse side; they could vaguely make out a hidden picture when the work was held up to light. But 25 years ago, when conservators finally peeled off its thick paper backing, art historians were astounded by the ugliness of the secret portrait of Cleopatra that was revealed.

The drawing that had been concealed for centuries showed the Ptolemaic ruler in a grotesque state of anguish, with her bulging, blank eyes looking forward and her mouth gracelessly agape, baring big teeth. Perhaps even more puzzling was the poor draftsmanship of the sketch. Michelangelo knew how to how to make stylishly tormented figures, so why was this one so especially ugly? At least one art historian thinks the reverse drawing is merely misattributed to the Renaissance master, and may have been sketched by his student instead. [Faux Real: A Gallery of Art Forgeries]

The lovelier Cleopatra portrait was known to have been made for a handsome young Roman nobleman Tommaso de' Cavalieri, with whom Michelangelo struck up a friendship in 1532. Writing for ARTnews, William E. Wallace, of Washington University in Saint Louis, says Cavalieri may have tried his hand at drawing a classicized head, perhaps based on an antique sculpture, during a lesson with Michelangelo.

When the student's drawing foundered, the teacher may have stepped in, according to Wallace's version of events.

"To demonstrate 'buon disegno' (good design), Michelangelo reversed the sheet and performed a miracle of artistic alchemy: ugliness became beauty, harrowing but unbecoming emotion became serene resignation, an indecorous head was transformed into a doomed Cleopatra," Wallace writes.

Both sides of the artwork are set to go on display this month at Boston's Museum of Fine Arts as part of an exhibition of the Italian master's drawings, called "Michelangelo: Sacred and Profane." The show, which was organized by the Muscarelle Museum of Art at the College of William & Mary in Williamsburg, Va., brings together 11 drawings of figures and 14 architectural designs by Michelangelo, including his unrealized plan for San Giovanni dei Fiorentini, a church in Rome.